DESCRIPTION (PI's abstract): The vestibular ocular reflex (VOR) is crucial for normal vision because it stabilizes images on the retina during normal head movements. The visual capability of patients with disorders affecting the VOR is severely impaired by blurred and double vision, and by oscillopsia. Normal head movements involve angular and translational components, both of which must be compensated for by the VOR. The angular VOR or AVOR has been well characterized by previous studies, but the translational VOR or TVOR has received attention only recently. Unlike the AVOR, which has a fixed response amplitude and direction relative to the rotatory stimulus, the amplitude and direction of the TVOR depends on the location of the viewed image relative to each eye and the head translation. The central goal of this proposal is to determine the neurophysiological mechanisms that are used to transform the translational vestibular afferent signal, derived from the otolith organs, into an appropriate compensatory motor command to the extraocular muscles. In order to accomplish this goal, we will focus on two aspects of signal processing in the primate's vestibular nucleus: (1) A comprehensive analysis of vestibular and oculomotor signal processing in vestibular nucleus neurons under a variety of behavioral conditions and vestibular stimuli. This part of the study will focus on dynamic characterization of vestibular signals, convergence properties of otolith and canal signals, and on the relationship between vestibular and eye movement signals encoded by each neuron. (2) The principal output neurons of the VOR are secondary vestibular neurons (currently called PVP units) and flocculus target neurons (FTNs). We plan to identify these cells behaviorally, and by electrical stimulation of the labyrinth or the cerebellar flocculus. After their identification, we will analyze the command signals delivered by these cells to motoneurons, and we will examine how these cells transform vestibular and eye movement inputs into the motor commands suitable to drive oculomotoneurons. We will pay particular attention to how disjunctive TVOR responses are channeled by these output neurons. In doing these studies, we will employ a new linear sled/rotator developed to our specifications by Accutronics, Inc. This new instrument will enable us to deliver precisely controlled linear (in the horizontal plane) or angular stimuli (about a yaw axis) in any combination to experimental subjects.